铁腕 is usually used attributively: 铁腕人物 (an iron-fisted figure), 铁腕政策 (iron-fisted policy), 铁腕手段 (heavy-handed means). It carries an admiring-or-fearful tone — strong leadership crossing into authoritarianism, depending on context.
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Literally 'iron wrist' — the wrist is what controls a hand's grip, so an 'iron wrist' grips ruthlessly. Same image as English 'iron fist'.
